Ma Cong, Zhang Zixiang, Xu Lei, Rashid Sajid, Li Guibai, Graham Nigel, Yu Wenzheng
Key Laboratory of Drinking Water Science and Technology, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China; State Key Laboratory of Advanced Separation Membrane Materials, School of Environmental Science and Engineering, Tiangong University, Tianjin 300387, China.
Key Laboratory of Drinking Water Science and Technology, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China.
Water Res. 2025 Jun 22;285:124082. doi: 10.1016/j.watres.2025.124082.
The coagulation-ultrafiltration-nanofiltration (CUF-NF) treatment system is a promising approach for water treatment. However, the effects of phosphate on this system remain inadequately understood. In this study bench scale tests were conducted with both aluminium and iron salts using jar testing and membrane filtration, and a range of phosphate doses. Results in this study reveal that, in the CUF treatment stages, phosphate inhibits floc formation and reduces organic matter removal efficiency by competing for "active sites" and increasing the negative surface charge of flocs. Specifically, the flocculation index values decreased by 56 % for Fe³⁺ and 37 % for Al³⁺ as phosphate concentrations increased from 0 to 0.2 mM, leading to a reduction in dissolved organic carbon (DOC) removal from 34.4 % to 14 % due to phosphate interference. In contrast, the quality of NF effluent improved substantially as phosphate concentrations increased, with the NF reaching a maximum of 20.2 % DOC removal efficiency. At low phosphate concentrations (<0.05 mM), NF flux showed minimal change; however, at higher concentrations, a notable decline in NF flux was observed. Additionally, phosphate presence significantly reduced the formation potentials of trihalomethanes (THMFP) and haloacetic acids (HAAFP) in the NF effluent by over 80 % at 0.2 mM phosphate. This reduction may be attributed to the enhanced ability of the NF membrane to intercept low molecular weight organics, mainly due to the presence of macromolecules that CUF failed to remove. Furthermore, the presence of phosphate is thought to increase the electronegativity and hydrophilicity of the fouling layer on the NF surface, which in turn further enhances the rejection of negatively charged dissolved organic matter (DOM).This study provides a mechanistic understanding of how phosphate influences coagulation, floc formation, DOM removal, and membrane fouling within the CUF-NF treatment system. The findings offer valuable insights for optimizing the treatment of phosphate-containing raw waters using dual membrane processes with coagulation pretreatment in practical applications.
混凝-超滤-纳滤（CUF-NF）处理系统是一种很有前景的水处理方法。然而，磷酸盐对该系统的影响仍未得到充分了解。在本研究中，使用烧杯试验和膜过滤，对铝盐和铁盐以及一系列磷酸盐剂量进行了实验室规模的试验。本研究结果表明，在CUF处理阶段，磷酸盐通过争夺“活性位点”并增加絮体表面负电荷，抑制絮体形成并降低有机物去除效率。具体而言，随着磷酸盐浓度从0增加到0.2 mM，Fe³⁺的絮凝指数值下降了56%，Al³⁺的絮凝指数值下降了37%，由于磷酸盐的干扰，溶解有机碳（DOC）去除率从34.4%降至14%。相比之下，随着磷酸盐浓度的增加，纳滤出水水质显著改善，纳滤的DOC去除效率最高达到20.2%。在低磷酸盐浓度（<0.05 mM）下，纳滤通量变化最小；然而，在较高浓度下，观察到纳滤通量显著下降。此外，在0.2 mM磷酸盐浓度下，磷酸盐的存在显著降低了纳滤出水中三卤甲烷（THMFP）和卤乙酸（HAAFP）的生成潜力超过80%。这种降低可能归因于纳滤膜截留低分子量有机物的能力增强，这主要是由于存在CUF未能去除的大分子。此外，磷酸盐的存在被认为会增加纳滤膜表面污垢层的电负性和亲水性，进而进一步增强对带负电荷的溶解有机物（DOM）的截留。本研究提供了关于磷酸盐如何影响CUF-NF处理系统内的混凝、絮体形成、DOM去除和膜污染的机理理解。这些发现为实际应用中使用混凝预处理的双膜工艺优化含磷原水的处理提供了有价值的见解。
